Final answer:
The action taken by the nurse when upholding a client's right to make and act on a choice is best described as supporting, which respects the client's autonomy, dignity, and independence.
Step-by-step explanation:
When a nurse upholds a client's right to make a choice and to act on that choice, the nurse is primarily engaging in supporting the client's autonomy. This support is fundamental to the ethical practice of nursing and respects the client's dignity and independence. It is essential that nurses not only inform clients about their choices but also support clients in whatever decisions they make, as long as those decisions do not cause harm to the clients or others.